ghuinness

I can't remember where I read it or heard it, but I thought there was speculation on some connection with the group "Black September". Date was significant in some way for that group.

edited: Found it:

September 6 and 9.

At the beginning of September 1970, the activities of the leftist Palestinian organizations in Jordan turned into open defiance of King Hussein himself. On September 1, a failed attempt on Hussein's life was made while he was on his way to the Amman airport. On September 6, members of the Popular Front hijacked three planes: A Swissair plane and a TWA plane were hijacked to the airport in Zarqa, and an additional plane, belonging to Pan American, was hijacked to the Cairo airport. Three days later, a British plane was hijacked, and
brought down near Amman. The passengers were held hostage. The hijackers demanded the release of Palestinian prisoners in various countries. A spokesman for the Popular Front said in Beirut that the hijackings were carried out in order "to teach the Americans a lesson, because of their long-standing support of Israel."

Yasser Arafat did not condemn the hijackings, which aroused an international protest against the Palestinians. Hussein knew that the international community would now be more sympathetic toward a decisive battle against the Palestinian organizations, and that Nasser - who wanted to promote the Rogers Plan - would be less supportive. The Jordanian king quickly lost control of his kingdom.
At the height of the drama of the hijacked planes, the Palestinians declared the area of Irbid in the north of the country a "liberated region," and announced that they were preparing for "the showdown."